There is near universal acceptance of the view that gestural imitation plays an important role in the early cognitive and social development of the child. The role of vocal imitation is substantial in linguistic development. Vocal imitation is the principal vehicle for infants' learning of their "mother tongue," the phonetic inventory and the prosodic structure of their native language. Work from this laboratory has revised conceptions about the origins of gestural and vocal imitation in infancy. We previously established that infants can imitate facial gestures at birth. Our recent work has shown that infants imitate both mothers and strangers and that 6-week-old infants imitate from memory after a 24-hr delay, with implications for both social and cognitive development imitation between toddler peers was also demonstrated, including work showing that acts demonstrated by a peer in a daycare setting were subsequently imitated at home, thus showing memory and imitative generalization across change in context Our new findings on vocal imitation have established vowel imitation in 12-week-olds and revealed interesting developmental change between 12- and 2O-weeks of age. Experiments with nonspeech sounds demonstrated that vocal imitation is selective; infants imitated speech sounds but not nonspeech sounds that preserved certain spectral properties of human speech. These new empirical findings led to the formation of two new theories. Regarding gestural imitation, the new theory focuses on the motivation, meaning, and functional significance of gestural imitation. It embeds early imitation within a framework of infants' developing understanding of persons and social cognition. Regarding vocal imitation, the theory unites new findings in speech perception and speech production, with particular emphasis on how exposure to native-language input alters both speech perception and speech production. The studies proposed for the next funding period investigate both gestural and vocal imitation across a broad age span, from birth to 3 years of age. Although each of the domains has specific concerns guiding the design of the experiments, there are issues common to both. Examples of these common concerns are: (a) the origins and basis of infants' imitative abilities, (b) the nature of the stimulus most active in eliciting imitation, (c) the acts of experience and development on imitation, and (d) the functional significance and use of imitation. We here propose a series of interlocking experiments on imitation, its development, meaning, and function in the first three years of life. The studies have implications for theories of social, cognitive, and linguistic development.